Add new docs theme, and restructure (#978)

* Change documentation theme to 'furo'
* Update docs source for new theme
* Update index and split introduction
* Add a Getting Started section to the docs
* Rename getting started docs file
* Reorganise setup instructions
* Update usage sections for consistency
* Update docs references in main README
* Show release in sidebar

README.md

@@ -42,8 +42,8 @@ met. It is regularly tested on Debian and Ubuntu Linux, Windows, and macOS.
 The Releases page has a `.deb` package that should install on Mint, Ubuntu and Debian.
 
 You can also use the novelWriter [PPA](https://launchpad.net/~vkbo/+archive/ubuntu/novelwriter).
-For more details, check the [Linux](https://novelwriter.readthedocs.io/en/latest/setup_linux.html)
-setup chapter in the documentation.
+For more details, check the [Getting STarted](https://novelwriter.readthedocs.io/en/latest/int_started.html)
+section in the documentation.
 
 ### Windows 10+
 
@@ -55,11 +55,9 @@ versions. The installer includes Python 3.10 and the library dependencies.
 You can also download and install one of the minimal zip files from the
 [Releases](https://github.com/vkbo/novelWriter/releases) page or the
 [novelwriter.io](https://novelwriter.io/) website.
-The [documentation](https://novelwriter.readthedocs.io/) has detailed install instructions for
-[Linux](https://novelwriter.readthedocs.io/en/latest/setup_linux.html),
-[Windows](https://novelwriter.readthedocs.io/en/latest/setup_windows.html), and
-[macOS](https://novelwriter.readthedocs.io/en/latest/setup_mac.html).
-They are pretty straightforward.
+The [Getting STarted](https://novelwriter.readthedocs.io/en/latest/int_started.html) section of the
+documentation has detailed install instructions for these packages, and for installation via the
+Python Package Index.
 
 ## Project Contributions